MW ablation: From Theory to Practice
Prof. S.N. Goldberg, MD FSIR
Image-guided Therapy and Interventional Oncology Unit
Dept. of Radiology
Hadassah Hebrew University Medical Center, Ein Karem
MW ablation: From Theory to Practice
Clinical rationale, technology development,
performance characterization &
optimization
• Direct tumoricidal effect
• Minimal systemic effects
• Less invasive than surgery
• Less expensive than surgery
• Applicable to non-surgical candidates
Percutaneous Image-Guided Therapy:
Potential Benefits for the Oncology Pt.
Image-guided Tumor Ablation:
Expanding Clinical Applications
Acceptance
• Liver
• Kidney
• Lung
• Bone
Early Experience
• Head / Neck
• Breast
• Pancreas
• Prostate
• Adrenal
• Complete (large volume) ablation
• Reproducible, predictable coagulation volume
• Minimally invasive
• Minimal morbidity
• Quick and easy
• Less expensive than alternatives
Image-Guided Tumor Ablation:
Ideal system characteristics
Image-Guided Tumor Ablation:
State of the Art
• Currently, no widely-available method that satisfies all the requirements of an ideal ablation system
• Among thermal methods, there are limited data to suggest that one agent is more effective than another
• Often based upon operator preferences or technique
• Trade-offs must be made
» Completeness vs. time, aggressiveness, complexity, etc.
MW Ablation:
Potential Advantages
• Bigger ablation = Deeper penetration of energy
• Hotter = applicator temps. 120 - 140° C
• Faster ablation time
Ing. Nevio Tosoratti, PhD
R&D Manager
HS Hospital Service S.p.A.
"MW ablation: from theory to practice.
Clinical rationale, technological development, performance
characterization & optimization"
Rome, May 28th, 2013
University of Rome “La Sapienza
Dept. Of Electronic Engineering
• Coagulation performance strongly correlated to
tissue impedance
• Limitations on the maximum attainable
temperatures (no charring should occur!) and,
in turn, on the final ablation size
• Very limited extension of the direct heating zone
(few mm around electrode exposed tip):
sensitivity to heat sinking
• Long range distribution of delivered energy:
poor treatment confinement(risks in treating patients with pacemakers or metallic prosthesis,
possible skin burns on return pads, possible overstimulation of
nervous terminations)
• Limitations on simultaneous use of multiple
electrodes
Limitations of RFA
RF
electrode
Grounding pads
RF
Currents
•MWs are non ionizing EM radiations
(frequency ~ 1 GHz for clinical use)
•MWs induce electric dipoles rotation at the
atomic level, generating frictional heat.
•Remarkably larger active heating zone with
respect to RFs, simultaneously heated with
no propagation delay
•No current circulation! Poorly or non
conductive targets still responsive to MW
heating
•Enhanced response to MW heating in
“polar” substances, such as water
MWs: beyond limitations
E
+
-
+
-
+
-
Applied MW
electric field
Oscillating dipoles
Interstitial MW
antennaRadiating tipHeating pattern
Appearance of RF or MW-ablated tissue
RF
MW
Interstitial
applicatorActive tipHeating pattern
MW
y
x
zy
xy
xy
MWA: ex vivo coagulative performance
Ex vivo bovine liver, room
temperature
•Cost and technical complexity
Generating and controlling MW power effectively and safely for clinical use is more complicated and
expensive than for RFA
•Control over the heating pattern
Conventional MWA probes are heavily affected by back heating phenomena (COMET EFFECT), both
due to scarce control over reflected power (that is, the portion of MW power not absorbed by tissues and
propagating backwards) and due to remarkable power loss along the antenna feeding cable, turning into
severe shaft overheating.
•Invasiveness
Common technical remedies to the heating pattern control issues bring to a significant enlargement of the
probes size, making them unsuitable to percutaneous use.
These critical issues have not been properly addressed until recently: therefore, MWA has so far
played a minor role in IR, despite its huge potential.
MWA technology: critical issues
Comet effect
Picture courtesy of prof. M. Cavagnaro,
University of Rome “La Sapienza”, Dept.
Electronic Engineering
Coaxial cable
Direct wave
Reflected wave
Feed
Dielectric tip
Outer conductor
Inner conductor
Heating pattern
Reflected wave
PRE
B. Topal et al., EJSO, 36, 8 (2010) 725
POST
/4 Choke
Introducing
needle
Choked applicators
• Use of a quarter-wave impedance
transformer
• Effective entrapment of reflected
waves
• Heating pattern confined to the
probe tip
• Transversal clearance remarkably
increased
• Not suitable for percutaneous use
Coaxial
cable
Radiating tip
Ellipsoidal
radiation diagram
Coaxial
connector
Metal
sleeve
/4 Choke
Introducing
needle
Conventional
Choke design
MINI-CHOKE
design
The mini-choke concept
• Worldwide patent (CNR, Dr I.
Longo) licensed to HS
• Effective as an ordinary choke
in trapping reflections, but with
no gauge increase
• Minimum insertion depth
required
Radiation
diagram
The mini-choke works!
Pictures courtesy of prof. M. Cavagnaro, University of Rome “La Sapienza”, Dept.
Electronic Engineering
Mini-choked applicator
Unchoked applicator
(mm)
Electric field
(normalized)AMICA-PROBE (HS)
pMTA (MICROSULIS)
The mini-choke works!
Courtesy of:
UT BIORAD
Dr Vanni
Lopresto
unchoked
The mini-choke works!
with mini-choke
I. Longo, G. Biffi Gentili, M. Cerretelli, N. Tosoratti, “A coaxial Antenna with Miniaturized Choke for Minimally
Invasive Interstitial Heating”. IEEE Trans. on Biomed. Eng. Vol 50 N. 1; 2003.
The mini-choke works!
Enhanced control over the probe radiation and heating pattern:
improved sphericity index, reduced risk of overheating damage
0
0,2
0,4
0,6
0,8
1
0 50 100 150 200 250
Ind
ex
of
sp
heri
cit
y (
D/L
)
Deposited Energy (kJ)
Avg 0.73
PRE-
POST-
Courtesy of Dr Solbiati-
12min/80W
HCC 4cm
6X5cm
Picture courtesy of Dr T. De Baere, IGR,
Villejuif, France
Ceramic tip
20 mm
Choke section Cooling chamber
Metallic
penetration point
5 mm
Metal ring
AMICA-PROBE: beyond the mini-choke
Frequency of operation: 2450 MHz (same as MW
ovens)
Interstitial 11G, 14G, 16G models
150, 200, 270mm shaft lengths
Mini-choke for reflections trapping
Internal cooling to avoid shaft
overheating: pre-assembled hydraulic lines
Lesions from 2cm to >5cm attainable through
different ablation time and power settings (up to
100W/net on probe)
Probe shaft (with anti-adherent coating)
New Ablation Device: Key ??
• What can it do ?
• Is it safe ?
• Is it better than other alternatives ?
Typical Results: Satisfaction of Search
Them ?!?! (4.9 ± 0.2 x 7.8 ± 0.4 cm) US !!!!
(5.7 ± 0.2 x 6.5 ± 1.7 cm)
New Ablation Device: Key ??
• What can it do ?
» Systematic application-specific characterization and
optimization
• Is it safe ?
• Is it better than other alternatives ?
Ex-vivo In-vivo
MWA: Systematic Characterization
RF Ablation:
Effect of Tumor Environment
Kidney Subcutaneous LungCVS; RF @90°C; 5 min Ahmed; Radiol 2004
Systematic Evaluation !!!
Materials and Methods:
• 110 ablations performed in ex-vivo bovine liver
» HS R&D
• Representative settings in in-vivo porcine liver
» Hadassah (n=20)
• 26 patients with small focal HCC nodules
(2.3±0.9cm; 1.3-4.5 cm) receiving single
applications of MW energy
» Solbiati / Meloni groups
Ex-vivo Studies:
• Systematically varied to create grids:
» Power (20 – 130 Watt net on antenna)
» Time (3 - 30 min) of energy application
• Key End-points:
» ablation diameter
» length
» sphericity index
HS Evaluation Means Business !!
Gladius Hispanicus ???
Coagulation Measurement:
Results summary: Ablation Size: Average Diameter (mm)
Ablation Time
(min)
Ablation Power (W)
20 40 60 80 100 130
315.7 19.7 25.3 32.0 35.7 36.3
520.0 27.3 33.7 37.2 38.0 42.3
1027.3 36.0 40.3 45.7 48.3 53.0
1532.7 41.7 48.0 55.0 57.0 59.8
2033.7 45.0 50.0 58.0 59.3 70.7
3041.0 52.3 58.3 65.0 69.0 72.3
Ex-vivo: Diameter vs. Time POWER (W)
Ex-vivo: Length vs. TimePOWER (W)
For the Mathematicians:
Results summary:
Index of Sphericity: Average(D/L) (mm)
Ablation
Time (min)
Ablation Power (W)
20 40 60 80 100 130
3 0.7 0.7 0.7 0.7 0.7 0.6
5 0.8 0.8 0.7 0.7 0.7 0.6
10 0.9 0.7 0.8 0.7 0.7 0.6
15 0.9 0.8 0.8 0.8 0.7 0.6
20 0.9 0.8 0.7 0.8 0.7 0.8
30 0.9 0.9 0.7 0.7 0.7 0.7
MW Sphericity vs. Power & Time:
In-vivo Results: (The Fate of All Good Swine in Israel)
Ablation
power (W)
Ablation
time
(min)
Diameter
(cm)Length (cm)
Index of
sphericity(N)
100 10 5.0 ± 0.3 8.5 ± 0.4 0.59 5
100 5 3.3 ± 0.5 5.9 ± 0.6 0.57 4
60 10 3.1 ± 0.5 4.9 ± 1.0 0.64 8
Results: In-vivo
Mining Relevant Clinical Data:
• Local control of focal hepatic malignancies treated with
microwave ablation with a novel high-power applicator
system: 14- ni ecneirepxe htnom108 patients
» L. Solbiati et al.
• Thermal ablation of primary and secondary liver tumors
using microwave energy: evaluation of technique
effectiveness and complications in 54 patients
» Meloni F, et al.
Pt. AV HCC VI cm 3.0 03/08/2010
MW: 14G, 10 min, 70 W
Necrosis : cm 5.7 x 3.7 x 4.2
Results: Summary
60 W / 10 min
HCC: 100 W / 10 min
Results: Summary
100 W / 10 min
EX VIVO
IN VIVO_PORCINE
PATIENT_HCC
New Ablation Device: Key ??
• What can it do ?
» Systematic application specific characterization and
optimization
• Is it safe ?
» Understand technology and perform appropriate pre-
clinical and clinical studies
• Is it better than other alternatives ?
MW Ablation: Safety
• Fact: MW ablation can proceed at temperatures
measuring 120 - 140° C
• Question: Is this a good thing or a bad thing ?
1 cm
T=12 minutes; P=65 watts
Micrablate Triaxial antenna
MWA: Ablation Around Vessels
Case Courtesy of Fred Lee Jr. MD
T=6 minutes; P=100 watts
Microsulis 5.7 mm antenna
MWA: Conduction of Steam
MW Ablation: Safety
• Fact: MW ablation can proceed at temperatures
measuring 120 - 140° C
• Question: What does this mean to adjacent
tissues ?
MW Ablation: Safety
• High temperature Effecting Adjacent Tissues
• What is the safe distance to prevent perforation of:
» Vessels
» Bronchi
» Gut (colon / small bowel / stomach)
» Ureters
» Bile ducts / GB
New Ablation Device: Key ??
• What can it do ?
» Systematic application specific characterization and
optimization
• Is it safe ?
» Understand technology and perform appropriate pre-
clinical studies and initial beta-site series
» Post-launch data accrual - registry
• Is it better than other alternatives ?
Initial Clinical Series:
• Local control of focal hepatic malignancies treated with
microwave ablation with a novel high-power applicator
system: 14- ni ecneirepxe htnom108 patients
» L. Solbiati et al.
• Thermal ablation of primary and secondary liver tumors
using microwave energy: evaluation of technique
effectiveness and complications in 54 patients
» Meloni F, et al.
LARGE LESIONS (>3cm)
MW
B. A. HCC VIII cm 4.0
MW: 14G, 12 min, 80 W
Necrosis : cm 6.6 x 5.1 x 4.9
PRE-
POST-
7-month f/u
B.M. HCC IV-VIII cm 4.9
MW: 14G, 13 min, 60 W
Necrosis : cm 5.4 x 5.1PRE - POST-
8-month f/u
2 antennas (3 cm spaced)
MW 14 G 10 min 50 W
Necrosis: 7.1 x 5.5 x 5.3 cm
L.M. HCC 6 x 4.5 cm
PRE-
POST-
V. C. 3 metastases from colon CAMW 14G
Met VIII 3.9 cm Met VIII 1.4 cm Met LTP VII 3.0 cm
60 W 11 min 45 W 10 min 45 W 9 min
Necrosis: 5.3 x 4.3 cm 5.1 x 3.9 cm 4.6 x 3.5 cm
PRE-
POST-
LESIONS ADJACENT to
LARGE BLOOD VESSELS
MW
Pictures courtesy of Dr Luigi Solbiati,
Head of the Radiology Dept., Hospital of Busto Arsizio
T.C. HCC VII cm 2.1
MW 14G 7 min, 50 W
Necrosis : cm 4.6 x 4.0 x 4.2
PRE-
POST-
R. M. HCC IV-VIII cm 1.6
MW 14G 4 min, 40 W
Necrosis : cm 4.0 x 3.0 x 3.6
PRE-
POST-
S. C. metastases from breast CA
14/07/2010 VII cm 4.5 MW 14G 16 min (2) 60 W 4.7 x 3.4 cm
V cm 1.7 MW 14G 6 min 40 W 4.2 x 3.8 cm
PRE-
POST-
New Ablation Device: Key ??
• What can it do ?
• Is it safe ?
• Is it better than other alternatives ?
New Ablation Device: Key ??
• Is it better than other alternatives ?
“If you ain’t the first kid on the block,
they’ll hold you to higher standards.”
Philosopher Eric von Sonnenberg
Tumor Ablation Registry:
• Pooling of data
» Efficacy in different organ systems
» Assessment of complications
» Differences in technique
• Identifying areas requiring / providing fertile further research
• Helping design pivotal randomized trials
» Best parameters / technique
» Most likely to succeed patient populations
• Caveat - asking the right questions
Ablation Evaluation: Doing It Right
• Systematic, tissue specific optimization:
» Ex-vivo tissues In-vivo animal studies clinical validation
• Demonstration of safety
» Animal studies Registry
• Application specific clinical validation
» Registry Comparative clinical trials
HS AMICA: making a long story short…
•2001: Mini-choke patent deposited by CNR
•2003: Mini-choke patent exclusively licensed to HS.
•2004: First prototypes of mini-choked, internally cooled MWA probes realized by HS.
• 2005: First prototype of a solid state, programmable 2450MHz/100W generator for clinical
use realized by HS
• 2006: HS AMICA receives CE approval. Available probes: 14G and 17G, mini-
choke+internal cooling, open-ended structure
• 2007/2008: First clinical trial on BPH patients. Probe re-engineering: moving to a closed-
point structure
• 2009: HS AMICA receives FDA approval. Early clinical experience in liver, lung, kidney
and bone ablation
2013:Over 10,000 procedures performed worldwide with HS AMICA (percutaneous, laparoscopic,
intra-surgical).
Almost 300 HS AMICA systems installed in more than 20 countries in Europe, Middle East
and America
AMICA-PROBE: technical validation
1) I.Longo, G. Biffi Gentili, M.Cerretelli, N.Tosoratti; “A Coaxial Antenna With Miniaturized
Choke for Minimally Invasive Interstitial Heating”, IEEE Trans. on Biomed. Eng., 50 82 (2003)
2) M. Cavagnaro, C. Amabile , P. Bernardi, S. Pisa, N. Tosoratti; “Design and Realization of a
New Type of Interstitial Antenna for Ablation Therapies”, Proceedings of the 39th European
Microwave Conference (2009)
3) M. Cavagnaro, C. Amabile , P. Bernardi, S. Pisa, N. Tosoratti; “A Minimally Invasive Antenna
for Microwave Ablation Therapies: Design, Performances, and Experimental Assessment”,
IEEE Trans. on Biomed. Eng. 58 949 (2011)
4) V. Lopresto, R. Pinto, G. A. Lovisolo, M. Cavagnaro; “Changes in the dielectric properties of
ex vivo bovine liver during microwave thermal ablation at 2.45 GHz”, Phys. Med. Biol. 57 2309
(2012)
AMICA-PROBE: pre-clinical validation
1) Bartoletti, T.Cai, N.Tosoratti, C.Amabile, A.Crisci, G.Tinacci, N.Mondaini, P.Gontero,
S.Gelsomino, G.Nesi; “In vivo microwave-induced porcine kidney thermoablation: results and
perspectives from a pilot study of a new probe”, BJU Int., 106 1825 (2010)
2) F.Meloni, A.Andreano,G.Bovo, B.Chiarpotto,C. Amabile, S.Gelsomino, S.Lazzaroni, S.Sironi;
“Acute Portal Venous Injury After Microwave Ablation in an In Vivo Porcine Model: A Rare
Possible Complication”, J Vasc Interv Radiol, 22 947 (2011)
3) O. Planche, C. Teriitehau, S. Boudabous, J. M. Robinson, P. Rao, F. Deschamps, G. Farouil, T.
de Baere; “In Vivo Evaluation of Lung Microwave Ablation in a Porcine Tumor Mimic Model”,
Cardiovasc. Intervent. Radiol., 2013 Feb; 36(1):221-8.
4) R Hoffmann, H Rempp, L Erhard, G Blumenstock, PL Pereira, CD Claussen, S Clasen;
“Comparison of Four Microwave Ablation Devices: An Experimental Study in ex Vivo Bovine
Liver”, Radiology 121127; published online February 25, 2013
AMICA-PROBE: clinical validation
1) R.Bartoletti, T.Cai, G.Tinacci, I.Longo, A.Ricci, M.P.Massaro, N.Tosoratti, E.Zini, N.Pinzi; “Transperineal
Microwave Thermoablation in Patients with Obstructive Benign Prostatic Hyperplasia: A Phase I Clinical Study
with a New Mini-Choked Microwave Applicator”, J of Endourol. 22 1509 (2008)
2) G. Zanus, R. Boetto, E. Gringeri, A. Vitale, F. D’Amico, A. Carraro, D. Bassi, P. Bonsignore, G. Noaro, C.
Mescoli, M. Rugge, P. Angeli, M. Senzolo, P. Burra, P. Feltracco, and U. Cillo; “Microwave Thermal Ablation for
Hepatocarcinoma: Six Liver Transplantation Cases”, Transplantation Proceedings, 43 1091 (2011)
3) O. M. Hetta, N. H. Shebrya, S. K. Amin; “Ultrasound-guided microwave ablation of hepatocellular carcinoma:
Initial institutional experience”, The Egyptian Journal of Radiology and Nuclear Medicine, 42 343 (2011)
4) T.Livraghi, F.Meloni, L.Solbiati, Giorgio Zanus; “Complications of Microwave Ablation for Liver Tumors:
Results of a Multicenter Study”, Cardiovasc. Intervent. Radiol., 35 868 (2012)
5) R Bartoletti, E Meliani, A Simonato, P Gontero, G Berta, P Dalla Palma, E Leonardi, T Cai, G Carmignani.
“Microwave-induced thermoablation with Amica-probe is a safe and reproducible method to treat solid renal
masses: results from a phase I study”. Oncol Rep. 2012 Oct; 28(4):1243-8
6) G Poggi, B Montagna, P Di Cesare, G Riva, G Bernardo, M Mazzucco, A Riccardi. “Microwave Ablation of
Hepatocellular Carcinoma Using a New Percutaneous Device: Preliminary Results”. Anticancer Res. 2013
Mar;33(3):1221-1227
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